The present invention relates to production of a semiconductor device and, more particularly, to a method of producing a semiconductor device which requires a fine gate electrode.
In recent years, large-scale integration of semiconductor devices and reduction of the design rules have remarkably progressed, and simultaneously, the gate electrodes of MOSFETS and the like have been required to have a fine size. A polysilicon layer is formed on an Si substrate via a gate oxide film, and the gate oxide film is patterned. In this case, the gate electrode is formed utilizing photolithography. The tolerance of dispersion in size has become more severe with the requirement for a so-called xe2x80x9chalfxe2x80xa2micronxe2x80x9d or xe2x80x9cquarterxe2x80xa2micronxe2x80x9d size.
FIG. 3 is a cross-sectional view for illustrating patterning of a polysilicon gate electrode according to a conventional method of producing a semiconductor device. A polysilicon layer 33 is formed on an Si substrate 31 via a gate oxide film 32. A resist layer 35 for a photolithographic process is formed on the polysilicon layer 33. In this case, practically, a natural oxide film 34 is present on the polysilicon layer 33. Thus, the resist layer 35 is coated onto the natural oxide film 34 on the polysilicon layer 33, followed by patterning.
In the case in which the polysilicon layer is patterned by the photolithographic process while the natural oxide film is present on the polysilicon layer, the patterning size of the resist layer varies depending on the state of the natural oxide film. Thus, the etching size of the polysilicon after the processing also varies. After all, the dispersion in size of the gate electrode becomes remarkable. Thus, the dispersion may depart from a required tolerance in size of the gate electrode.
In view of the above-described situations, the present invention has been devised, and an object of the present invention is to provide a method of producing a semiconductor device by which the dispersion in size of the gate electrode can be reduced.
The method of producing a semiconductor device of the present invention which includes a process of patterning a gate electrode on a polysilicon layer formed on an Si wafer using photolithography is characterized in that the patterning process contains a process of removing a natural oxide layer formed on the polysilicon layer as a pre-treatment for coating a resist by the photolithography. Also, the method of producing a semiconductor device of the present invention is characterized in that the process of removing the natural oxide film uses fluorine or a fluorine-containing compound.
According to the method of producing a semiconductor device of the present invention, the natural oxide film having an arbitrary thickness formed on the polysilcon layer is removed before the resist is coated. Thereby, the uniform state on the whole surface of the polysilicon layer is obtained.